As known, the respiratory system, comprising lungs and thoracic cage, works as a pump that rests on a muscle called the diaphragm, which coordinates air and oxygen suction/exhalation actions. In natural ventilation a contraction of the diaphragm produces a vacuum in the lungs so that air is inspired. However, problems of respiratory insufficiency caused by thoracic cage or lungs pathologies, as well as problems of insufficient ventilation revealed by the rise of carbon dioxide in arterial blood beyond physiological values, can affect the correct operation of the respiratory system. Then, for increasing or restoring a natural ventilation in an individual in poor health, a mechanical ventilation must be applied that consists of delivering pressurized air in the aerial ducts (also known as the airways or air passages) and then in the lungs of the patient by means of a special apparatus.
A largely used technique for treatment of patients with chronic pulmonary pathologies or with acute respiratory insufficiency is Non-Invasive Mechanical Ventilation (NIMV). NIMV assures a much lighter work to respiratory muscles, improves gaseous exchanges and in most cases avoids the need of an intratracheal intubation, which is much more invasive and can cause lesions or infections of the respiratory system, as well as it can be applied only in a hospital.
An apparatus for non-invasive mechanical ventilation comprises usually a fan, which produces air at a certain pressure, and a nasal mask, which is connected to the fan by means of a flexible tube. Furthermore, pneumatic instruments are provided that control the air delivery on the basis of pressure data measured in real time, which are responsive to the respiration of the patient or are set in a predetermined pressure program.
Non-invasive ventilation with positive pressure has two particular approaches, one with fixed pressure (CPAP) and another with two levels of pressure, or bi-level (BiPAP). In particular, the BiPAP is a kind of ventilation characterized by two different levels of pressure, which exchange with each other at a predetermined interval and allow passive pulmonary ventilation responsive to changes of intrapulmonary pressure. At the same time the patient can breath spontaneously at each step of the respiratory cycle without any mechanical support. More in detail, the apparatus for ventilation delivers an inspiration positive air pressure (IPAP), by means of a fan when breathing in, and an exhalation positive air pressure (EPAP), which is also positive but less than the previous. In other words, during the mechanical ventilation, the apparatus accomplishes the respiratory work necessary to ventilate the lungs. Usually, the EPAP is only slightly more than the atmospheric pressure whereas the IPAP is much higher.
However, in the existing apparatus the air pressure supplied to the patient follows a predetermined profile depending on a program, on the kind of fan and on the kind of control chosen, and said profile hardly would fit the peculiar needs of an individual. In fact, the set limit values are IPAP and EPAP and only adjustable value is the pressure of air supplied between the two limit values, by a valve or alternatively by controlling the fan power.
Furthermore, such apparatus can assure ventilation and air exchange only to the main aerial ducts without reaching the peripheral aerial ducts, and this fact could lead to atrophy of the latter. This drawback has also the consequence of a very long time before reaching a natural respiration rate of the patient after a temporary trauma.